Atomic force microscope (AFM) is a kind of scanning probe microscope (SPM). AFM is a high-precision measurement instrument in which a force necessary for the interaction such as an attractive or repulsive force between a sharp probe and a sample surface is used to analyze the sample surface with resolution on atomic-level. Atomic force microscopy has recently attracted much attention as a promising method for hyper-fine pattern formation. A general application of AFM is to shape the surface of a sample without damaging the sample.
When a force is applied to damage the surface of a sample to some extent, atomic and molecular arrangements on the sample surface can be manipulated. This technique is termed ‘nanolithography’. An artificial nanostructure can be constructed on the surface of a sample using nanolithography to control physical parameters (such as electron density and energy level) of the sample on a nanometer scale.
Various methods associated with the use of AFM are currently being investigated in the field of nanolithography, for example, a method for forming a hyper-fine pattern using a resist material and a method for forming an oxide pattern on the surface of a hydrogen-passivated Si-wafer or poly-Si by an electric field of an AFM tip. Nanolithography combined together with electrostatic force microscopy (EFM) and scanning capacitance microscopy (SCM) can be used for next-generation database applications.
The mechanism of the formation of an oxide pattern using an AFM is briefly summarized as follows. An organic thin film of a predetermined thickness is formed on a silicon substrate and a voltage of several volts is applied locally to the organic thin film using an AFM tip to form an oxide pattern. A resist layer of the portion of the organic thin film to which the voltage has been applied is crosslinked. During the crosslinking, Si atoms react with moisture in the air to form SiOx, which protrudes from the resist thin film. This reaction mechanism is shown below (see J. Vac. Sci. Technol. A14 (3), 1996, 1223).
(Reaction Mechanism)
AFM Tip (Cathode Reaction)2nH2O+2ne−→nH2+2nOH−
Silicon Substrate (Anode Reaction)Si+nH2O→SiOn+2nH++2ne−
However, the silicon oxide can be etched at a much higher rate than the other portions because of its very loose structure. The portion of the organic thin film to which the voltage has not been applied is dissolved in a developing solution and the portion to which the voltage has been applied remains undissolved as a pattern.
Factors considered to be important in AFM lithography are an applied voltage, an electric current, a scan rate, a humidity, etc. If lithography is performed under non-optimal conditions to form a pattern, the line width of the pattern is irregular and the pattern line is disconnected. A better pattern can be formed when a high-performance resist is used and the lithography conditions (including an applied voltage, a scan rate, a humidity, etc.) are optimized. The formation of a uniform thin film is also very important.
The present invention has succeeded in developing a high-sensitivity, high-resolution resist that can be applied to a large-area substrate by spin coating in an easy manner and can be patterned to have a line width of 0.1 μm or less. A further improvement of optimum processing conditions using the resist material will enable the formation of hyper-fine pattern whose line width is in the order of a few nanometers. Therefore, it is anticipated that technology associated with the use of the resist material would provide an important base for the development of terabit-scale semiconductor memories and other device applications, including displays and nano-biodevices, based on ultra-thin film patterning techniques.
The present invention features the applicability as a resist for both e-beam lithography and for AFM lithography. A photosensitive resist (or a photosensitive polymer) is an organic photosensitive material that is necessarily used in the manufacturing processes of a variety of high-precision electronic information industrial products. A photosensitive resist is a generic term for polymer composition systems that absorb incident light or radiation energy and undergo physicochemical changes. Resists for the processing of hyper-fine shapes are important materials that are currently used in advanced printing, semiconductor and electronic information industries. Resists are widely used as photocurable materials and photosensitive materials for surface coating and pattern formation.
AFM-based lithographic processes and resists used therefor are well known in the literature (Small, 2006, 2, 481-484, S. Jegadesan; S. Valiyaveettill, Easy Writing of Nanopatterns on a Polymer Film Using Electrostatic Nanolithography and Langmuir 2006, 22, 3807-3811, Subbiah Jegadesan; Prasad Taranekar; Swaminathan Sindhu; Rigoberto C. Adrincula; Suresh Valiyaveettil, Electrochemically Nanopatterned Conducting Coronas of a Conjugated Polymer Precursor; SPM Parameters and Polymer Composition Journal of Nanoscience and Nanotechnology, 2007, 7, 2172-2175, S. Jegadesan; S. Sindhu; S. Valiyaveettil, Fabrication of Nanostructure on a Polymer Film Using Atomic Force Microscope).
The present inventor has developed 1,3-bis(trimethylsilyl)isopropyl methacrylate (BPMA) as a silicon-containing monomer and filed a patent application (U.S. Ser. No. 08/942,249 published on September 1999). Further, the present inventor has developed and reported resists using the monomer (J. Photopolymer. Science and Technology, No. 4, Vol. 10, 1997, Kang, Y. J., Lee, H. et al. Chemically Amplified Silicon Containing Resist for ArF Excimer Laser Lithography, p 585; Mol. Cryst. Liq. Cryst., 1999, 327, Kim, Y. D., Lee, H. et al. New Bilayer Positive Photoresists for 193 nm Photolithography, p. 279; and Korean Patent Registration No. 10-1999-230417 published on Nov. 15, 1999).
Further, the present inventor has developed a compound substituted with a fluoroalkylsulfonium salt as a photoacid generator and a copolymer thereof (Korean Patent No. 0637450 and PCT/KR 2006/000535), and a compound having fluoroalkylsulfonium salts as photoacid generators introduced into the side chain of the compound, and a homopolymer thereof (Korean Patent No. 0823471). Thereafter, the present inventor has earnestly and intensively conducted research to develop a resist copolymer with higher sensitivity and resolution than the known copolymer, and finally accomplished the present invention.